In situ application of etch back for improved deposition into high-aspect-ratio features

ABSTRACT

A continuous in situ process of deposition, etching, and deposition is provided for forming a film on a substrate using a plasma process. The etch-back may be performed without separate plasma activation of the etchant gas. The sequence of deposition, etching, and deposition permits features with high aspect ratios to be filled, while the continuity of the process results in improved uniformity.

BACKGROUND OF THE INVENTION

[0001] One of the primary steps in the fabrication of modernsemiconductor devices is the formation of a thin film on a semiconductorsubstrate by chemical reaction of gases. Such a deposition process isreferred to as chemical vapor deposition (“CVD”). Conventional thermalCVD processes supply reactive gases to the substrate surface whereheat-induced chemical reactions take place to produce a desired film.Plasma-enhanced CVD (“PECVD”) techniques, on the other hand, promoteexcitation and/or dissociation of the reactant gases by the applicationof radio-frequency (“RF”) energy to a reaction zone near the substratesurface, thereby creating a plasma. The high reactivity of the speciesin the plasma reduces the energy required for a chemical reaction totake place, and thus lowers the temperature required for such CVDprocesses as compared to conventional thermal CVD processes. Theseadvantages are further exploited by high-density-plasma (“HDP”) CVDtechniques, in which a dense plasma is formed at low vacuum pressures sothat the plasma species are even more reactive.

[0002] As semiconductor device geometries have decreased in size overthe years, the ratio of the height of such gaps to their width, theso-called “aspect ratio,” has increased dramatically. Gaps having acombination of a high aspect ratio and a small width present a challengefor semiconductor manufacturers to fill completely. In short, thechallenge usually is to prevent the deposited film from growing in amanner that closes off the gap before it is filled. Failure to fill thegap completely results in the formation of voids in the deposited layer,which may adversely affect device operation, such as by trappingundesirable impurities.

[0003] One process that the semiconductor industry has developed toimprove gapfill capability uses a multistep deposition and etchingprocess. Such a process is often referred to as adeposition/etch/deposition (“dep/etch/dep”) process. Such dep/etch/depprocesses divide the deposition of the gapfill layer into two or moresteps separated by a plasma etch step. The plasma etch step etches theupper corners of the first deposited film more than the film portiondeposited on the sidewall and lower portion of the gap, thereby enablingthe subsequent deposition step to fill the gap without prematurelyclosing it off Typically, dep/etch/dep processes can be used to fillhigher-aspect-ratio small-width gaps than a standard deposition step forthe particular chemistry would allow.

[0004] Notably, while there has been some recognition that in situ etchprocesses may be desirable for dep/etch/dep processes, in practiceattempts at such processes have been constrained by limitations in theeffectiveness of plasma processing systems. For example, one type ofplasma processing chamber places a wafer on an electrode of the plasmacircuit, opposite another planar electrode, and capacitively coupleshigh-frequency electrical power to the two electrodes to form a plasmabetween them. Such a plasma reactor has advantages where it is desirableto form the plasma in the presence of the substrate, such as when thephysical movement of plasma species to and from the substrate isdesired. However, the bombardment by plasma species that results fromthis type of plasma formation may be undesirable for dep/etch/depprocesses.

[0005] Another approach to plasma processing generates plasma in aremote location, and couples the plasma to a processing chamber. Varioustypes of plasma generators have been developed, including magnetronsources coupled to a cavity, inductively coupled toroidal sources,microwave irradiation directed at a plasma precursor, electron-cyclotronresonance generators, and others. Remote plasma techniques offer anumber of advantages for certain types of processes, such as cleaning,but generally the atomic species that eventually reach the chamber areof relatively low density because of recombination effects. Withdep/etch/dep processes, this may result in nonuniformities since the gasdistributions differ for the deposition and etching phases.

[0006] Inductively coupled plasma systems have been developed that cangenerate a high-density plasma locally above a wafer, but shield thewafer from the more deleterious effects of the plasma generation byusing the plasma itself as a buffer between the wafer and the plasmageneration region. These systems typically rely on diffusion of plasmato provide a uniform density across the wafer surface. In one system, adielectric dome, or chamber top, has a conductive coil would around thedome. High-frequency electric energy provided to the coil couples to aplasma precursor gas in the chamber and converts the precursor toplasma. The fields generated by the coil through the dome have anelectric field component normal to the surface of the dome that causesplasma species to be directed to and from the inner surface of the dome.This field component acting on the plasma can cause physical erosion ofthe inside of the dome, as well as affect the power coupling to theplasma to cause a nonuniform plasma density. The possibility of damageto the dome is further increased during the etch phase of a dep/etch/depprocess if the etch phase is performed in situ. This is because etchantspecies react chemically with the dome material, in additional to thephysical bombardment of the ionic etchant species.

[0007] It is, therefore, desirable to provide improved methods ofperforming dep/etch/dep processes that avoid the surface erosionproblems of conventional systems while taking greater advantage of thebenefits of having all phases of the dep/etch/dep processes performed insitu.

SUMMARY OF THE INVENTION

[0008] Embodiments of the invention thus encompass aspects of performingin situ dep/etch/dep processes. These embodiments are generallyconfigured as processes in which the etch-back may be performed withoutseparate plasma activation of the etchant gas. This feature results fromthe use of process chamber configurations that allow the in situ processto proceed through the phases of deposition, etch, and depositioncontinuously.

[0009] In one set of embodiments, a continuous in situ process isprovided using a plasma source disposed within the process chamber. Insuch embodiments, a first gaseous mixture is provided to the processchamber, from which a plasma is generated to deposit the first portionof the film. Thereafter, an etchant gas is flowed into the processchamber without terminating the plasma to etch the first portion of thefilm. Thereafter, a second gaseous mixture is provided to the processchamber without terminating the plasma to deposit the second portion ofthe film. As before, the gaseous mixtures may include silicon-andoxygen-containing gases to deposit a silicon oxide film, and the etchantgas may include a fluorine-containing gas such as NF₃ or F₂. Indifferent embodiments, bias power may or may not be used.

[0010] In other embodiments, the first deposition phase may be combinedwith the etch phase of the process by providing a gaseous mixture to theprocess chamber that includes both a deposition gas and an etchant gas.A plasma is generated from the gaseous mixture with a plasma couplingstructure to simultaneously deposit a first portion of the film on thesubstrate and etch the film. The plasma includes poloidal ion flow alongfield lines substantially parallel to a surface interior to the processchamber and disposed to separate the plasma from the plasma couplingstructure. The etchant gas acts chemically and can be controlled moreeasily than can, for example, the physical sputter component of ahigh-density-plasma deposition process. These embodiments thus providean improved level of control.

[0011] Subsequent to the combined deposition and chemical etching, asecond gaseous mixture having a second deposition gas may be provided tothe process chamber to deposit a second portion of the film. This seconddeposition gas may be substantially the same as the first depositiongas. The deposition gases may include a silicon-containing gas, such asSiH₄, and an oxygen-containing gas, such as O₂, to deposit a siliconoxide layer. The etchant gas may include a fluorine-containing gas, suchas NF₃ or F₂, which reacts with the deposited silicon layer.

[0012] Some embodiments of the invention additionally include applyingan electrical bias to the substrate during the combined deposition andetching phase. The power density for the electrical bias may besufficiently low, ≦3.2 W/cm², that the physical sputter component from ahigh-density plasma process is small. Instead, the bias acts tointroduce an anisotropy in the action of the etchant that improves theoverall deposition for certain features. In one embodiment, the biaspower density is between 0.9 and 1.6 W/cm².

[0013] The methods of the present invention may be embodied in acomputer-readable storage medium having a computer-readable programembodied therein for directing operation of a substrate processingsystem. Such a system may include a process chamber, a plasma generationsystem, a substrate holder, a gas delivery system, and a systemcontroller. The computer-readable program includes instructions foroperating the substrate processing system to form a thin film on asubstrate disposed in the processing chamber in accordance with theembodiments described above.

[0014] A further understanding of the nature and advantages of thepresent invention may be realized by reference to the remaining portionsof the specification and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a simplified diagram of one embodiment of a high densitychemical vapor deposition system according to an embodiment of thepresent invention;

[0016]FIG. 2 is a flow diagram illustrating one embodiment of acontinuous in situ dep/etch/dep process; and

[0017] FIGS. 3A-3E illustrate how a high-aspect-ratio feature may befilled with the procedure of FIG. 2.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

[0018] 1. Introduction

[0019] Embodiments of the invention use a continuous in situ plasma forall phases of a dep/etch/dep process. This is achieved with a chamberdesign that disposes the plasma source, which may be a toroidal plasmasource, within the process chamber. Such a design and process have anumber of advantages. For example, the chamber design is especiallysuitable for processes that use etchant gases because it does notinclude a capacitive coupling between the dome and plasma-generationcoils. This allows in situ processing with etchants while avoidingundesirable surface erosion within the process chamber. This process isunlike previous dep/etch/dep processes, which were instead generallyadapted for remote-plasma etch phases; attempts to adapt those processesto in situ etch phases resulted in the deficiencies described above.

[0020] In embodiments of the invention, the dep/etch/dep process isaccordingly performed as a continuous process without the need forseparate plasma generation in each of the individual phases. Thecontinuity of such a process results in increased process uniformityacross a wafer. In particular, such continuity results in the same gasdistribution for the deposition gases and for the etchant gas duringtheir respective phases. Thus, even if this distribution includes somedegree of nonuniformity, the multiple phases of the process tend tocompensate. In regions of a wafer where the deposition is greater(smaller) than average, the degree of etching is similarly greater(smaller) than average.

[0021] This process uniformity is further enhanced because the in situtoroidal configuration by itself tends to decrease the degree ofnonuniformity in all the gas distributions. The toroidal configurationproduces field lines predominantly parallel to, rather thanperpendicular to, the interior chamber surfaces separating the couplingstructure from the plasma. As a result, poloidal ion flow is providedwith symmetry about the central axis of the toroid, which contributes tothe improvements in process uniformity.

[0022] 2. Exemplary Substrate Processing System

[0023]FIG. 1 illustrates one embodiment of a plasma processing system 10suitable for a variety of plasma processes, such as plasma-enhanceddeposition processes and plasma etch processes. In one embodiment, itmay be used for a continuous dep/etch/dep process. In some embodiments,a high-density plasma may be generated from a gaseous mixture, where“high-density” is understood in this context to mean having an iondensity that is equal to or exceeds 10¹¹ ions/cm³. Plasma processingsystem 10 includes a chamber 12 having a chamber body 14 and a chambertop 16, a vacuum system 18, an RF generator (power supply) 20 coupled toa toroidal core 22 by leads 24, 26 by a coil (not shown). In oneembodiment the toroidal core 22 is a ferrite core, but could be othermagnetic material, or merely free space (“air”) depending on thecoupling structure. A bias plasma system 30 is optional for producingmovement in the plasma normal to the surface 32 of a substrate 34. Thesubstrate could be a silicon wafer, for example, or another substrate.For ease of description, the surface 32 is referred to as the “processsurface” of the substrate. It is understood that the process surface mayinclude layers and structures previously formed on the substrate. Incertain embodiments, the wafer is a silicon wafer with a nominaldiameter of 200 mm or 300 mm.

[0024] A gas delivery system 36 provides gas(es) to the processingchamber and other system components through gas delivery lines 38, onlysome of which might be shown. Typical gases provided by the gas deliverysystem 36 might include plasma precursor gases, such as a cleaning oretching plasma precursor gas, a plasma deposition precursor gas, plasmastriking gas, plasma dilution gas, and other gases, such as a cleaningprecursor gas provided to an optional remote plasma cleaning system 40,for example. The delivery lines generally include some sort of control,such as a mass flow controller 42 and shut-off valves (not shown). Thetiming and rate of flow of the various gases is controlled through asystem controller 44, as will be described in further detail below.

[0025] The chamber top 16 includes an outer shell 46, a toroid cover 48,an insulative spacer 50, and a bottom plate 60. The bottom plate 60 maybe shaped to provide a selected plasma density distribution. The outershell, toroid cover, and bottom plate can be made of aluminum, anodizedaluminum, stainless steel, or other material as appropriate for theintended processes to be performed. A surface coating can be applied tothe inner surfaces of some chamber components, if desired, to reduce thepotential for contamination of the substrate or chamber. The insulativespacer 50 is typically made from a dielectric material such as ceramic;examples include alumina-based ceramic or aluminum nitride, silicon, andfused silica. It is generally desirable that the insulative spacerprevent substantial induced current flow between the chamber body 14 andany electrically conductive parts of the chamber top 16. In a particularembodiment, the insulative spacer is high-alumina ceramic about 20 mmthick.

[0026] The toroid cover 48 contains a toroidal core 22. In oneembodiment the toroidal core is made of a ferrite material, such as amaterial sold under the trade designation “3F3” by ROYAL PHILIPSELECTRONICS, N.V., but other ferrites or materials, such as iron, orair, may be appropriate. The RF generator is coupled to the core bycoiling the leads 24, 26 around the core. Alternative and equivalentcoupling structures will be apparent to those skilled in the art.Although two leads are shown connecting the RF generator to the core, analternative circuit configuration using a single lead and common groundcould be used. Specifically, the RF generator could be mounted directlyon the chamber structure, thus avoiding long leads to the coil andassociated electromagnetic radiation, as well as reducing variations inload resulting from long leads and eliminating the RF matching network.The core, coil, and generated plasma form a transformer circuit thatoperates as a toroidal plasma source 28 within the processing chamberwhen in operation. The primary circuit of the transformer is the coil,with the plasma serving as the secondary circuit of the transformer, theprimary coupling to the secondary through the core.

[0027] The entire transformer (plasma source) is within the processingchamber. As described above, the outer shell 46 and chamber body 14 canbe made of a conductive material, thus serving as a shield forelectronic emissions generated by the toroidal plasma source 28. Thisnot only reduces unwanted emissions from the system, but also may allowthe RF generator 20 to operate at frequencies that would otherwisegenerate an unacceptable level of electronic noise emissions. In such anembodiment, it may be desirable to provide leads from the RF generatorto the chamber that are shielded. Additional shielding may beappropriate around dielectric elements, such as the insulative spacer.

[0028] In a preferred embodiment the leads are provided through atoroidal plasma source support structure, such as a spoke 62. Forexample, the leads could come through the bottom plate and then into thetoroidal cavity 64 containing the toroidal core 22. Alternatively,support for the toroidal plasma source could be provided by supportstructure(s) dropping down from the chamber top. In one embodiment (notillustrated in FIG. 1), four spokes support the toroidal core, shaped(center) portion 66 of the bottom plate 60, and toroid cover 48 in theinterior of the chamber 70. The cross section illustrated in FIG. 1 isconsistent with a 1, 3, 5, etc. spoke pattern. In an alternativeembodiment, the leads are brought through a feed-through (not shown) inthe outer shell 46 and through the toroid cover 48.

[0029] The chamber body 14 includes a substrate support member 72, whichis mounted on, and forms a continuous inner surface with, the body.Substrates are transferred into and out of chamber by a robot blade (notshown) through an insertion/removal opening (not shown) in the side ofthe chamber. Motor-controlled lift pins (not shown) are raised and thenlowered to transfer the substrate from the robot blade to the substratesupport member 72. A substrate receiving portion 74 of the substratesupport member can include a wafer hold-down apparatus, such as anelectrostatic chuck (not shown), that can selectively secure thesubstrate to the substrate support member during substrate processing,if desired. In one embodiment, the substrate support member 72 is madefrom anodized aluminum, aluminum, or aluminum oxide. The substratesupport member may also include a heater (not shown) to heat the waferduring processing, or to heat portions of the chamber during a cleaningprocess. In one embodiment, the substrate support member holds thesubstrate 36 so that the processing surface 34 of the substrate isopposite and essentially parallel to the major plane of the toroid. Thatis, the processing surface faces the loop described by the toroidalcore.

[0030] The vacuum system 18 includes throttle body 76, which housestwin-blade throttle valve 78 and is attached to gate valve 80 andturbo-molecular pump 82. It should be noted that throttle body 76 offersminimum obstruction to gas flow, and allows symmetric pumping, asdescribed in co-pending, commonly assigned U.S. patent application Ser.No. 08/712,724 entitled “SYMMETRIC CHAMBER” by Ishikawa, filed Sep. 11,1996, and which is incorporated herein by reference in its entirety forall purposes. The gate valve can isolate the turbo-molecular pump fromthe throttle body, and can also control chamber pressure by restrictingthe exhaust flow capacity when the throttle valve 78 is fully open. Thearrangement of the throttle valve, gate valve, and turbo-molecular pumpallow accurate and stable control of chamber pressures from about 1millitorr to about 2 torr. It is understood that other types of vacuumpumps and configurations of vacuum systems could be used withalternative embodiments of the present invention.

[0031] The RF generator 44 operates at a nominal frequency of 400 kHz,but could operate at different frequencies, such as 60 Hz, 2 MHz, 13.56MHz, 60 MHz, or 200 MHz among others, with appropriate design of theelements of the plasma system. The RF generator can supply up to 8 kW,but the processing system typically draws about 3-5 kW when processing a200-mm wafer. It is understood that lower or higher power levels mightbe appropriate according to the type of process being performed and thesize of the substrate.

[0032] A particular advantage of embodiments of the present inventionutilizing a ferrite core is the relatively low quality factor (“Q”) ofthe toroidal plasma generating structure 84, which includes the core,coil, and cover. The low Q also reduces the sensitivity of the plasmasystem to the chamber load, thus resulting in a more stable andconsistent plasma operated over a wider process range. In a high-Qsystem, the power delivered to the plasma can vary as the plasma isformed or chamber conditions change. For example, a plasma might beinitiated with a plasma striker gas, such as argon. When a precursorgas, such as NF₃ or F₂, is provided to the plasma, the dissociation ofthe gas into plasma creates a sudden increase in plasma species(pressure) as well as electrically charged particles. This effect canchange the load on the power supply as well as the match to the load,resulting in reduced power transfer to the plasma and potentiallyreflecting a harmful level of power back to the generator. In thepresent system, a low-Q configuration can be implemented, avoiding theseproblems.

[0033] A bias plasma system 30 includes a bias generator 86 and anoptional bias matching network 88. The bias plasma system capacitivelycouples the substrate receiving portion 74, i.e. the substrate, toconductive (grounded) inner surfaces of the chamber through a commonground 90. The bias plasma system serves to enhance the transport ofplasma species (e.g. reactive ions or other particles) created by theplasma generating structure 84 to the surface 32 of the substrate.

[0034] The gas delivery system 36 provides gases from several gassources 92, 94, 96, 98 to the chamber and other system components viathe gas delivery lines 38 (only some of which might be shown). Gases canbe introduced into the chamber in a variety of fashions. For example, atop port 100 is shown as one example of a means of flowing gases intothe chamber. A gas mixing chamber (not shown) can be present between thegas sources and the chamber, or the top port can be arranged with anumber of parallel or concentric gas conduits to keep various gasesseparate until reaching the chamber. In an alternate embodiment, gasconduits are present in the spoke(s) supporting the toroidal plasmagenerating structure 84 and nozzles (ports) are provided in the centerportion of the chamber top. In yet another alternative embodiment, a gasdelivery ring with a series of gas nozzles is provided about an innercircumference of the processing chamber. If gas ports are provided inthe outer perimeter portion 102 of the bottom plate 60, then it isgenerally desirable that the outer perimeter portion extend beyond theedge of the substrate, to reduce the chance of particles forming at theouter perimeter portion falling on the surface of the substrate.

[0035] An optional remote plasma cleaning system 104 is provided toclean deposition residues from chamber components periodically. Thecleaning system includes a remote microwave or RF generator 106 thatcreates a plasma from a cleaning gas source 98 such as molecularfluorine, nitrogen trifluoride, other fluorocarbons, or equivalents in areactor cavity 108. The reactive species resulting from this plasma areconveyed to the chamber interior through cleaning gas feed port 110 viaapplicator tube 112.

[0036] The system controller 44 controls the operation of the plasmaprocessing system 10. In a preferred embodiment, the system controllerincludes a processor 114 coupled to a memory 116, such as a hard diskdrive, a floppy disk drive (not shown), and a card rack (not shown). Thecard rack may contain a single-board computer (SBC) (not shown), analogand digital input/output boards (not shown), interface boards (notshown), and stepper motor controller boards (not shown). The systemcontroller is coupled to other parts of the processing system by controllines 118 (only some of which might be shown), which may include systemcontrol signals from the controller and feedback signals from thesystem. The system controller conforms to the Versa Modular European(VME) standard, which defines board, card cage, and connector dimensionsand types. The VME standard also defines the bus structure having a16-bit data bus and 24-bit address bus. System controller 44 operatesunder the control of a computer program 119 stored on the hard diskdrive or other computer programs, such as programs stored on a floppydisk. The computer program dictates, for example, the timing, mixture ofgases, RF power levels and other parameters of a particular process. Theinterface between a user and the system controller is via a monitor (notshown), such as a cathode ray tube (CRT), and a light pen (also notshown).

[0037] It is specifically understood that other types of chambers mightbe adapted to a toroidal plasma source according to the presentinvention, and that different types of wafer support systems, such as acenter pedestal, might be used, as well as different exhaustconfigurations, such as a perimeter exhaust configuration. Inparticular, additional coils might be added to control the plasmadensity and distribution (uniformity) inside the processing chamber. Forexample, instead of the metal outer shell described in conjunction withFIG. 1, a dielectric dome or shell could be used, and a coil providedoutside the chamber, or a coupling structure(s), such as a pole face ofa solenoid, could couple to the interior of the chamber through achamber wall. Similarly, additional coils or other coupling structurescould be provided within the chamber to manipulate the plasma. Suchcoils might lie above, below, or essentially coplanar with the toroidalplasma source. Additional embodiments for the substrate processingsystem are set forth in U.S. patent application Ser. No. 09/584,167,filed May 25, 2000 by Michael S. Cox et al., entitled “TOROIDAL PLASMASOURCE FOR PLASMA PROCESSING,” the entire disclosure of which is hereinincorporated by reference in its entirety for all purposes.

[0038] Other substrate processing systems may alternatively be used. Oneexample of a system that may incorporate certain of the subsystems androutines described above and which may be adapted for performing methodsin accordance with the invention is the ULTIMA™ system, manufactured byAPPLIED MATERIALS, INC., of Santa Clara, Calif. Further details of sucha system are disclosed in the copending, commonly assigned U.S. patentapplication Ser. No. 08/679,927, filed Jul. 15, 1996, entitled“Synmmetric Tunable Inductively-Coupled HDP-CVD Reactor,” having Fred C.Redeker, Farhad Moghadam, Hirogi Hanawa, Tetsuya Ishikawa, Dan Maydan,Shijian Li, Brian Lue, Robert Steger, Yaxin Wang, Manus Wong and AshokSinha listed as co-inventors, the entire disclosure of which isincorporated herein by reference. These systems are discussed forexemplary purposes only. It would be a matter of routine skill for aperson of skill in the art to select an appropriate conventionalsubstrate processing system and computer control system to implement thepresent invention.

[0039]3. In Situ Deposition/Etch/Deposition Process

[0040] The in situ dep/etch/dep process used in embodiments of theinvention may be understood with reference to FIGS. 2 and 3A-3E. FIG. 2shows a flow chart of an exemplary plasma process used in one embodimentto deposit a film on a substrate with stepped surfaces forming gaps withan aspect ratio as large as 6:1-7:1, and having a width less than about0.1 μm. The substrate is loaded into the process chamber 12 through avacuum-lock door onto the substrate receiving portion 74 at block 210.The substrate has a process surface essentially facing and parallel tothe toroidal plasma source 28. Once the substrate is properlypositioned, gas flows are established at block 214 to stabilize thepressure, which is maintained throughout the first deposition of thefilm by manipulating the throttle valve 78 with a stepper motor whilethe vacuum system 18 pumps at a constant capacity. In one embodiment,the pressure is maintained at a value less than 50 mtorr. Whenestablishing gas flows at block 214, a nominal source bias (e.g. 10 W)may be applied.

[0041] Once gas flows and pressure are established, the bias RF ispreset at block 218, a relatively low power (e.g. 300 W) being used toestablish proper operating conditions. A toroidal source power of, forexample, 3000 W is applied within the chamber at block 222 to strike theplasma. After the plasma has been struck, the toroidal source power, RFbias, and gas flows are adjusted to the desired deposition conditions atblock 226. The deposition gas may include, for example, SiH₄ and O₂ forthe deposition of silicon oxide; it may additionally include sources offluorine (e.g., SiF₄), boron, phosphorus, carbon, and/or nitrogen, amongothers, to deposit doped silicon oxides. The configuration of thetoroidal plasma source 28 with respect to the process surface creates apoloidal plasma with theta symmetry, i.e. rotational symmetry about acentral axis essentially normal to the process surface (the “toroidaxis”). After being struck, the plasma is sustained by power from thetoroidal plasma source 28. In alternative embodiments, the plasma may bestruck from an inert plasma striker gas, such as argon, which is easilyionized to form a stable plasma.

[0042] After deposition of the first portion of the film, an etchant gasis flowed into the process chamber at block 230 to etch part of thedeposited first portion. Where the deposited material is a siliconoxide, the etchant gas may include a source of fluorine atoms, such asC₃F₈, CF₄, NF₃, or F₂, among others. Because the design of theprocessing system is particularly suitable for in situ etchingprocesses, the etchant may be provided without termination of theplasma. The flow of deposition gases is halted and the etchant gassupplied as a continuous process. In one embodiment, the flows aremaintained as distinct flows, with the plasma being maintained by flowof an inert gas such as argon.

[0043] In another embodiment, the deposition and etchant flows overlapso that both deposition and etchant gases are provided simultaneously toprocess chamber 12. The plasma includes poloidal ion flow along fieldlines substantially parallel to a surface, such as bottom plate 60, thatseparates the plasma from the coupling structure. The overlapping flowsmay be provided for the entire deposition period so that no initialdeposition phase distinct from the etching phase is provided. Providingsuch an overlap has the effect of producing a process that hassimultaneous deposition and etching properties. This simultaneity allowsfeatures with larger aspect ratios to be filled than do depositionprocesses alone.

[0044] In some ways, providing simultaneous deposition-gas and etchantflows mimics the deposition behavior of HDP-CVD deposition processes. InHDP-CVD processes, it is common to introduce an inert sputtering agent,such as argon, into the deposition gas mixture, causing the process toproduce both deposition and sputtering components. An importantdifference between this HDP-CVD process and the combined deposition andetching process used with the in situ processes of the invention is thatthe sputtering component is physical while the etching component ischemical. In particular, in typical HDP-CVD processes, the sputteringarises from bombardment of the substrate by ionic plasma species.According to the embodiment of the invention that uses simultaneousdeposition and etching, however, the etching arises from a chemicalreaction between the etchant ionic species and the substrate material.

[0045] Further, while the sputtering provided by HDP-CVD depositionprocesses may act act anisotropically, there may be redeposition. Thisis to be contrasted with performing an etching process, which generallyhas no redeposition. Accordingly, the effect of the HDP sputteringcomponent is limited in gapfilling features with larger aspect ratios.The deposition material still forms with a characteristic breadloafingshape that leads to the formation of voids in the deposited layer.

[0046] In embodiments of the invention that use an etchant species,however, anisotropic etching can be provided by adding a bias with thebias plasma system 30 and exploiting the chemical nature of thereaction. Since chemical etching acts to reopen the gap, etchinganisotropy can increase the efficiency of this process. A sufficientbias power to produce a reasonable anisotropic etching component for a200-mm wafer is 300 W (corresponding to a bias power density of about0.9 W/cm²). An upper limit for the bias power is approximately 1000 W(corresponding to a bias power density of about 3.2 W/cm²), at whichpoint physical sputtering becomes significant. In one embodiment thebias power is limited to the range 300-500 W (corresponding to a biaspower density of 0.9-1.6 W/cm²).

[0047] Such nonisotropic etching may also be used by itself as part ofthe dep/etch/dep process, when the first deposition proceedsindependently of the second deposition. After the etching phase at block230, residue from the etchant gas may optionally be removed at block232. Where the etchant gas comprises a fluorine-containing gas, suchresidue may include fluorine atoms deposited on surfaces within theprocess chamber. Removal of such residue may be performed by flowing,for example, O₂, Ar, or an O₂+Ar combination. Subsequently, orimmediately after the etching phase at block 230 if the optional removalis not performed at block 232, deposition gases are again provided tothe process chamber 12 at block 234 to deposit the second portion of thefilm. Again, by using the chamber design described above, it is possibleto transition effectively between the etching phase of block 230 to thedeposition phase of block 234 without terminating the plasma.

[0048] The deposition of the film with the above-described dep/etch/depprocess is illustrated schematically in FIGS. 3A-3E. FIG. 3A shows afeature 300 on a substrate that is to be gapfilled. The results of aprior-art process that simply uses a deposition procedure is shown bythe right arrow to FIG. 3B. The deposited layer 304 has a characteristicbreadloafing shape that produces voids 306. If the dep/etch/dep processof the invention is used instead, the downwards arrow to FIG. 3C showsthe result after a first deposition step such as provided by block 226.The amount of material deposited is small enough that layer 308, whileshowing the characteristic breadloafing, has not yet pinched off a void.The result of the etch step of block 230 is shown in FIG. 3. Afteretching layer 308, perhaps including a bias to perform the etchanisotropically, the profile of the resulting layer 310 mimics that ofthe original feature 300, but is less severe. Accordingly, the seconddeposition phase of block 234 can fill the feature completely, as shownin FIG. 3E.

[0049] Having fully described several embodiments of the presentinvention, many other equivalent or alternative methods will be apparentto those of skill in the art. These alternatives and equivalents areintended to be included within the scope of the invention, as defined bythe following claims.

What is claimed is:
 1. A method for depositing a film on a substrate ina process chamber, the method comprising: providing a first gaseousmixture to the process chamber; generating a plasma from the firstgaseous mixture with a plasma source disposed within the process chamberto deposit a first portion of the film on the substrate; thereafter,flowing an etchant gas into the process chamber without terminating theplasma to etch part of the first portion of the film; and thereafter,providing a second gaseous mixture to the process chamber withoutterminating the plasma to deposit a second portion of the film on thesubstrate.
 2. The method recited in claim 1 further comprising applyingan electrical bias to the substrate while flowing the etchant gas. 3.The method recited in claim 2 wherein the bias has a power densityapproximately between 0.9 W/cm² and 3.2 W/cm².
 4. The method recited inclaim 1 wherein the second gaseous mixture is substantially the same asthe first gaseous mixture.
 5. The method recited in claim 1 wherein thefirst and second gaseous mixtures each include a silicon-containing gasand an oxygen-containing gas, and wherein the etchant gas includes afluorine-containing gas.
 6. A method for depositing a film on asubstrate in a process chamber, the method comprising: providing a firstgaseous mixture to the process chamber, the first gaseous mixturecomprising a first deposition gas and an etchant gas; and generating aplasma from the first gaseous mixture with a plasma coupling structureto simultaneously deposit a first portion of the film on the substrateand etch the film, wherein the plasma includes poloidal ion flow alongfield lines substantially parallel to a surface interior to the processchamber and disposed to separate the plasma from the plasma couplingstructure.
 7. The method recited in claim 6 further comprising providinga second gaseous mixture to the process chamber without terminating theplasma, the second gaseous mixture comprising a second deposition gas,to deposit a second portion of the film.
 8. The method recited in claim6 further comprising applying an electrical bias to the substrate. 9.The method recited in claim 8 wherein the bias has a power densityapproximately between 0.9 W/cm² and 3.2 W/cm².
 10. The method recited inclaim 8 wherein the bias has a power density approximately between 0.9W/cm² and 1.6 W/cm².
 11. The method recited in claim 6 wherein theplasma is a high-density plasma.
 12. The method recited in claim 6wherein the second deposition gas is substantially the same as the firstdeposition gas.
 13. The method recited in claim 6 wherein the firstdeposition gas includes a silicon-containing gas and anoxygen-containing gas, and wherein the etchant gas includes afluorine-containing gas.
 14. A computer-readable storage medium having acomputer-readable program embodied therein for directing operation of asubstrate processing system including a process chamber; a plasmacoupling structure; a substrate holder; and a gas delivery systemconfigured to introduce gases into the process chamber, thecomputer-readable program including instructions for operating thesubstrate processing system to form a film on a substrate disposed inthe process chamber in accordance with the following: providing a firstgaseous mixture to the process chamber, the first gaseous mixturecomprising a first deposition gas and an etching gas; generating aplasma from the first gaseous mixture with the plasma coupling structureto simultaneously deposit a first portion of the film on the substrateand etch the film, wherein the plasma includes poloidal ion flow alongfield lines substantially parallel to a surface interior to the processchamber and disposed to separate the plasma from the plasma couplingstructure.
 15. The computer-readable storage medium recited in claim 14,the computer-readable program further including instructions forapplying an electrical bias to the substrate.
 16. The computer-readablestorage medium recited in claim 14, the computer-readable programfurther including instructions for providing a second gaseous mixture tothe process chamber without terminating the plasma, the second gaseousmixture comprising a second deposition gas, to deposit a second portionof the film.
 17. A computer-readable storage medium having acomputer-readable program embodied therein for directing operation of asubstrate processing system including a process chamber; a plasmageneration system having a plasma source disposed within the processchamber; a substrate holder; and a gas delivery system configured tointroduce gases into the process chamber, the computer-readable programincluding instructions for operating the substrate processing system toform a film on a substrate disposed in the process chamber in accordancewith the following: providing a first gaseous mixture to the processchamber; generating a plasma from the first gaseous mixture with theplasma source; thereafter, flowing an etchant gas into the processchamber without terminating the plasma to etch part of the first portionof the film; and thereafter, providing a second gaseous mixture to theprocess chamber without terminating the plasma to deposit a secondportion of the film on the substrate.
 18. The computer-readable storagemedium recited in claim 17, the computer-readable program furtherincluding instructions for applying an electrical bias to the substratewhile flowing the etchant gas.
 19. A substrate processing systemcomprising: a housing defining a process chamber; a plasma generatingsystem operatively coupled to the process chamber and includeding aplasma coupling structure disposed within the process chamber; asubstrate holder configured to hold a substrate during substrateprocessing; a gas-delivery system configured to introduce gases into theprocess chamber, including sources for a silicon-containing gas, afluorine-containing gas, and an oxygen-containing gas; apressure-control system for maintaining a selected pressure within theprocess chamber; a controller for controlling the plasma generatingsystem, the gas-delivery system, and the pressure-control system; and amemory coupled to the controller, the memory comprising acomputer-readable medium having a computer-readable program embodiedtherein for directing operation of the substrate processing system, thecomputer-readable program including instructions to control thegas-delivery system to provide a first gaseous mixture to the processchamber, the first gaseous mixture comprising a first deposition gasthat includes the silicon-containing gas and the oxygen-containing gasand an etchant gas that includes the fluorine-containing gas; andinstructions to control the plasma generating system to generate aplasma from the first gaseous mixture to simultaneously deposit a firstportion of the film on the substrate and etch the film, wherein theplasma includes poloidal ion flow along field lines substantiallyparallel to a surface interior to the process chamber and disposed toseparate the plasma from the plasma coupling structure.
 20. Thesubstrate processing system recited in claim 19, the computer-readableprogram further including instructions for applying an electrical biasto the substrate.
 21. The substrate processing system recited in claim19, the computer-readable program further including instructions forproviding a second gaseous mixture to the process chamber withoutterminating the plasma, the second gaseous mixture comprising a seconddeposition gas, to deposit a second portion of the film.
 22. A substrateprocessing system comprising: a housing defining a process chamber; aplasma generating system operatively coupled to the process chamber, theplasma generating system including a plasma source disposed within theprocess chamber; a substrate holder configured to hold a substrateduring substrate processing; a gas-delivery system configured tointroduce gases into the process chamber, including sources for asilicon-containing gas, a fluorine-containing gas, and anoxygen-containing gas; a pressure-control system for maintaining aselected pressure within the process chamber; a controller forcontrolling the plasma generating system, the gas-delivery system, andthe pressure-control system; and a memory coupled to the controller, thememory comprising a computer-readable medium having a computer-readableprogram embodied therein for directing operation of the substrateprocessing system, the computer-readable program including instructionsto control the gas-delivery system to provide a first gaseous mixture tothe process chamber; instructions to control the plasma generatingsystem to generate a plasma from the first gaseous mixture with theplasma source to deposit a first portion of the film on the substrate;instructions to control the gas-delivery system to flow, thereafter, anetchant gas into the process chamber without terminating the plasma toetch part of the first portion of the film; and instructions to controlthe gas-delivery system to provide, thereafter, a second gaseous mixtureto the process chamber without terminating the plasma to deposit asecond portion of the film on the substrate.
 23. The substrateprocessing system recited in claim 22, the computer-readable programfurther including instructions for applying an electrical bias to thesubstrate while flowing the etchant gas.